The present teachings are generally directed to devices and methods for entangled photon triplet generation, and in particular to on-chip integrated sources for generating direct entangled photon triplets.
An efficient triplet-photon source can have a variety of applications ranging from fundamental experiments in quantum optics to strict tests of quantum theory to revolutionary applications in secure quantum communication and computation. Quantum entanglement, where multiple particles share a joined quantum state, is the basis for many of these applications. Secure two-party quantum communication links using optical fiber (at telecommunications wavelengths, e.g. λ=1550 nm) have recently been commercialized using pairs of entangled photons. The challenge for realizing a multiparty quantum network is to entangle three or more photons, including the ability to form a Greenberger-Horne-Zeilinger (GHZ) state.
The production of direct entangled photon triplets has, however, proven to be exceedingly difficult. Although there are different ways to entangle photons (e.g., using post-selection methods), direct entangled photon triplet production differs in that the photon triplets originate from the same original photon and are generated in the same event.
Current methods for entangled photon triplet generation have primarily focused on adapting photon pair sources. For example, in one process known as cascaded spontaneous parametric down-conversion (SPDC), a single photon splits into two photons through SPDC (a χ(2) nonlinear process) and one of those photons splits a second time, forming a triplet. SPDC can achieve conversion pair efficiencies in the range of 10−9-10−6 (which translates to triplet efficiencies of 10−18-10−12 using cascaded SPDC). Direct triplet production through a χ(3) process, known as third-order spontaneous parametric down-conversion (TOSPDC), whereby one photon is annihilated to produce a photon triplet, is less explored due to extraordinarily low efficiency in bulk materials. The small efficiency is due to low χ(3) nonlinearitities (compared to χ(2) processes), poor photon confinement, and difficulties achieving momentum conservation (phase matching) between disparate wavelengths.
Accordingly, there is a need for enhanced sources and methods for generating entangled photon triplets.